1. Field of the Invention
The present invention relates to a downhole valve assembly. In particular, the present invention relates to a downhole valve assembly that provides a contingency/back-up device in the event that another downhole valve has failed to open.
2. Description of the Related Art
Well completion involves various downhole procedures prior to allowing production fluids to flow thereby bringing the well on line. One of the downhole procedures routinely carried out during well completion is pressure testing where one downhole section of the well is isolated from another downhole section of the well by a closed valve mechanism such that the integrity of the wellbore casing/liner can be tested.
Well completion generally involves the assembly of downhole tubulars and equipment that is required to enable safe and efficient production from a well. In the following, well completion is described as being carried out in stages/sections. The integrity of each section may be tested before introducing the next section. The terms lower completion, intermediate completion and upper completion are used to describe separate completion stages that are fluidly coupled or in fluid communication with the next completion stage to allow production fluid to flow.
Lower completion refers to the portion of the well that is across the production or injection zone and which comprises perforations in the case of a cemented casing such that production flow can enter the inside of the production tubing such that production fluid can flow towards the surface.
Intermediate completion refers to the completion stage that is fluidly coupled to the lower completion and upper completion refers to the section of the well that extends from the intermediate completion to carry production fluid to the surface.
During testing of the intermediate completion stage the lower completion is isolated from the intermediate completion by a closed valve located in the intermediate completion. When the integrity of the tubing forming the intermediate completion section is confirmed the upper completion stage can be run-in.
Generally the completion stages are run-in with valves open and then the valves are subsequently closed such that the completion stages can be isolated from each other and the integrity of the production tubing and the well casing/wall can be tested.
Typically, the valves remain downhole and are opened to allow production fluids to flow. By opening the valves the flow of production fluids is not impeded.
In the event that a valve fails to open, for example where the valve or an actuating mechanism operable to open the valve becomes jammed, remedial action is generally required because a failed valve effectively blocks the production path.
Remedial action often involves removing the valve. The valve may be removed by milling or drilling the valve out of the wellbore to provide a free flowing path for production fluid.
It will be appreciated that resorting to such remedial action can result in costly downtime because production from the well is stopped or delayed. The remedial action may result in damage to the well itself where milling or drilling the valve or valves from the wellbore may create perforations in the production tubing or the well casing or well lining. As a result such actions would preferably be avoided.
It is desirable to provide a downhole device such that production downtime due to a failed valve is reduced.
It is further desirable to provide an improved downhole valve assembly that helps to avoid using remedial actions such as milling or drilling to remove a failed valve from an intermediate or upper completion section of a wellbore.
It is desirable to provide a downhole valve assembly that provides a contingency or back-up system when there is a failed valve located in the wellbore.